In the current study, 76.1% of the participants were found to be vitamin D deficient, which was higher than the figures reported in other studies. Age, blood sugar levels, and cholesterol were significant factors associated with vitamin D status in Saudi men.
Despite the higher serum 25OHD cut-off (75 nmol/L) used in the current study, the prevalence of vitamin D deficiency among this cohort of Saudi males was higher in comparison to other studies conducted in Saudi Arabia. Most of these studies have used a cut-off ranging from 25 nmol/L to 50 nmol/L, and the prevalence of vitamin D deficiency among Saudi Males ranged from 17.7 to 87.8% [10,11,12,13]. Using the most commonly used cut-off of 50 nmol/L, the prevalence of vitamin D deficiency in the present study would have been 52.1%. The higher prevalence of vitamin D deficiency reported in the current study highlights that though vitamin D deficiency in Saudi Arabia is still high, there is no evidence of any interventions to decrease these high figures. The higher prevalence of vitamin D deficiency may not be limited to developing countries as reported by Lenders et al., where vitamin D deficiency is common in as many as one half of the middle-aged to elderly subjects .
Age was one of the significant correlates of serum vitamin D levels in our study cohort. The vitamin D levels were lowest in the younger age group, which significantly increased until they reached the highest level in the older age group. These results are in agreement with earlier studies [10, 12, 15] conducted in Saudi Arabia and other countries, where young individuals are more likely to have insufficient levels of vitamin D, with the highest prevalence of vitamin D deficiency observed in the 20–30 years old age group . On the other hand, Smotkin-Tangorra et al.  and Orwell et al.  concluded that higher prevalence of vitamin D deficiency was associated with older age and was more common in older males. It is a paradox, most of our respondents (79%) are exposed to sun daily; why younger males who are apparently healthy, have higher sunlight exposure, and engage in outdoor activities and exercises, have a higher prevalence of vitamin D deficiency. One explanation may be that older adults take supplements that contain vitamin D. However, this might not be the only reason and hence further large-scale studies to investigate this phenomenon are required.
With respect to the blood sugar levels, the mean vitamin D serum levels were higher amongst non-diabetic individuals in our study, which is in contrast to other studies that show higher levels of 25OHD in subjects with DM compared to non-diabetic individuals [19,20,21,22,23]. This may be attributed to medications that are used to treat DM which have been associated with enhancing circulating levels of 25OHD . Earlier reports have shown that vitamin D may help regulate the production of insulin in the pancreas. It is supposed that body’s sensitivity to insulin is enhanced by vitamin D, which in turn minimizes the risk of insulin resistance that is often the precursor to diabetes type 2. Adjusting the levels of vitamin D in the blood to around 60–80 ng/ml can aid in maintaining the blood glucose levels under control, which is vital for diabetic patients . Population studies suggested a positive correlation between low vitamin D levels with an increased possibility of developing type 2 diabetes. Hence, people with higher levels of vitamin D may have a low probability to develop type 2 diabetes .
Data on the association between cholesterol and vitamin D shows varied results. Population studies indicate that people with lower levels of vitamin D are more likely to have higher cholesterol levels. In 2012, a study showed that vitamin D supplements had no cholesterol lowering effects at least in the short term, and then too only low-density lipoproteins levels may increase. On the other hand, a study in 2014 found that taking calcium and vitamin D supplements together enhances cholesterol levels in postmenopausal overweight or obese women . The study conducted in Pakistani Immigrants taking daily vitamin D supplementation of 10 or 20 μg for 1 year did not show any change in their lipid profile .
Our results indicated no significant association of BMI with vitamin D levels. Baradaran et al. reported results similar to our study , in contrast to earlier studies where vitamin D levels were found to be negatively correlated to BMI in both obese and non-obese population [30, 31].
Though our study has some interesting findings, it has certain limitations. First, it was a cross-sectional, hospital-based study and therefore, we could not assess causality. In addition, this might have exposed the study to some sources of bias resulting from the manner in which study subjects were recruited or due to differences arising due to the participants’ cultural background, age, and socio-economic status. However, participants in the current study referred to the King Saud University Medical City were not limited to the capital city of Riyadh as all neighboring areas and governments centers refer to this tertiary hospital. This makes the selection of cases devoid of bias and could be considered representative of the Saudi population. Second, the sample size was relatively small and the dietary intake was not assessed. The study did not take into consideration the difference in sunlight exposure arising due to seasonal variation though, given the availability of sunshine nearly throughout the year, the seasonality might not be a significant factor in our case. However, the study addressed the significantly high deficiency of vitamin D amongst participants living in a country where they are exposed to sunny environment and high temperature throughout the year.